Design And Physical Properties Of New Silicon And Si-Ge Alloy Materials

Silicon element and its compounds play an indispensable role in modern industry and have been widely used in various related fields.This paper adopts the method of atoms doped,looking for a new type of silicon allotrope and silicide structure,combined with the first principles calculation method to study the mechanical properties of the new structure under the normal pressure,elastic anisotropy,electronic structure and other properties,and also analyzes the affecting factor on the changes of band,providing theoretical basis for effective synthesis of the material,It also provides support for the theoretical research of other new materials.The main contents of this paper are as follows:1.The physical properties with superhard carbon materials of G21,G58,G90,G117,G158,G164 and G223 were studied.TheVickers hardness values of these carbon materials are all larger than 40 GPa.The mechanical and dynamic stability of seven kinds of superhard carbon materials were studied by calculating the elastic constants and phonon spectra.The calculation results of volume modulus and shear modulus show that these seven kinds of superhard carbon materials have stronger compressive resistance than that of diamond.The calculation of B/G ratio and Poisson's ratio shows that these superhard carbon materials are brittleness.As can be seen from the band structure,the seven kinds of superhard carbons are all direct semiconductors,and their band gaps range from 2.84 eV to 4.36 eV.2.A new silicon allotrope of o-Si32 was proposed based on the previous study of direct band gap superhard carbon materials,and its physical properties were investigated under atmospheric pressure.The lattice constants and densities of the structure were calculated based on first principles.o-Si32 has mechanical and dynamic stability at 0 GPa.The calculated results of bulk modulus and shear modulus show that o-Si32 has strong resistance to compression deformation.The B/G ratio and Poisson's ratio of o-Si32indicate that the structure has strong ductility.In order to better study the electronic structure of o-Si32,the band structure of o-Si32 was calculated by using PBE and HSE06functional respectively,and the band gaps are 0.682 eV and 1.261 eV,respectively.3.The physical properties of Si_36-xGe_x(x=1?18,36)alloys have been systematically studied.The lattice constant and densities of Si_36-xGe_x(x=1?18,36)alloys have been calculated based on first principles,and the effect of the doping amount of Ge atom on the lattice parameters has been analyzed.Phonon spectrum calculation results show that the alloys materials were calculated with dynamics stability.The elastic constants of Si_36-xGe_x(x=1?18,36)alloys were calculated,the results show that the alloy materials with mechanical stability,and with the increment of germanium atom with its elastic constants decrease gradually.At the same time,the bulk modulus,shear modulus and Young's modulus of Si_36-xGe_x(x=1?18,36)alloys decrease with the increasing of the content of Ge atom,which indicates that the compressive deformation resistance of Si_36-xGe_x(x=1?18,36)alloys were gradually weakened.Finally,the electronic structure of Si_36-xGe_x(x=1?18,36)alloys were studied in this paper.From the calculation results of the band structure,the band gap value of the alloys decreased gradually with the addition of Ge atom,and the Si25Ge11,Si23Ge13,Si22Ge14,Si15Ge18 and Ge36 exhibit metallicity.Through the study of these new materials,and the result shows that they have excellent electronic structure,if can succeed in experiment preparation,then it will have a good application prospect in the field of modern industrial optoelectronics.With the emergence of more and more new materials,on the one hand,gave the researchers a lot of confidence,constantly perfect in theory;on the other hand,it also attracts more and more scholars to join the scientific research team.